In completing a hydrocarbon producing formation in a deep well, various completion techniques require that a tubing string be attached to a retrievable packer so that a tool string can be suspended from a vent string with the vent string being supported from the retrievable packer. In perforating the hydrocarbon producing formation of a borehole, for example, it has heretofore been necessary to utilize a wireline in order to open the perforated nipple of the vent string so that flow from the completed formation can flow up the tubing annulus into the perforated nipple, and up the production string to the surface of the earth.
In addition to the trip which must be made into the hole with the wireline in order to operate the vent string, it is often necessary to additionally employ a blanking plug in order to enable various other manipulative operations to be safely carried out on the borehole prior to the act of completion. Installation and retrieval of the blanking plug calls for two additional round trips to be made with a wireline operated fishing tool.
Making a trip into a borehole with a wireline is costly as well as dangerous because anything put into the hole is a calculated risk inasmuch as there is always a danger of losing the apparatus and hence a costly fishing job.
Where a conventional wireline operated perforated nipple is employed, there is sometimes more than 12,000 psi pressure differential across the sliding sleeve thereof and for this reason difficulty is often experienced in forcing the sliding sleeve to move to the open position by a wireline operated fishing tool. Moreover, in some well completion techniques, it is often desirable to perforate simultaneously with the opening of the perforated nipple. This expedient is not possible where a wireline is used to manipulate the vent string because a considerable time delay is experienced while the wireline is being removed from the borehole and before the perforating gun can be safely fired.
For these and many other reasons peculiar to well completion and well work-over operations, it is desirable to be able to run a packer downhole with a vent assembly being disposed in underlying relationship respective to the packer, and with the vent assembly supporting various downhole equipment, such as a jet perforating gun. It is desirable that such a vent assembly be actuated by manipulation of the tubing string in a manner whereby the final act of setting the packer also actuates the vent assembly to the opened position thereby enabling a flow path to be immediately established between a production zone and a surface flow line upon perforation of the hydrocarbon bearing formation.